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Name: Gina
Status: student
Age: 16
Location: N/A
Country: N/A
Date: 1999 

Could you please explain for me why a balloon filled with H2 or He has very little gas in it after 24 hours?

The rubber walls of a balloon are porous on a very microscopic scale. H2 and He are very light molecules, and they move very fast. They can pass through the walls of a balloon faster than other gases. A rubber balloon filled with air will also go flat, but more slowly.

Mylar balloons are less porous; a Mylar balloon, even when filled with helium, will stay inflated for a much longer time.

Richard E. Barrans Jr., Ph.D.

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